A core is a special, preformed part of a casting which is essential for complex and delicate shapes in the casting process. Around 95% of sand and 5% of binder are mixed as the raw material for manufacturing the core. Organic binders exhibit a high performance but generate contaminants and toxic gases since they are composed of toxic chemicals, and therefore, the trend in popular types of binder is evolving from organic to inorganic. In this context, we focus on the development of a discrete element model (DEM) model for the mixer in the core manufacturing process using an inorganic binder. We validate the developed model by comparing it with an actual horizontal mixer system. The actual mixer has dimensions of 1.36 m in length and 0.17 m in diameter. When the process is simulated once under the same operating conditions, the actual process run time is the same as the simulation run time. Based on this model, we carry out case studies by varying conditions such as the length of the mixer, and location of injection nozzle. As per our DEM study, the mixer length can be reduced by more than 20% relative to the existing design. We also suggest alternative mixer designs by optimizing the location of the injection nozzle.